基于字典的键创建新列？

Question

我试图在使用字符串文字和键的for字典项循环中的dataframe中创建一个新列，但它会抛出一条“ValueError:无法设置没有定义索引和标量的帧”错误消息

exp类别的字典定义

  d = {'Travel & Entertainment': [1,2,3,4,5,6,7,8,9,10,11], 'Office supplies & Expenses': [13,14,15,16,17],
    'Professional Fees':[19,20,21,22,23], 'Fees & Assessments':[25,26,27], 'IT Expenses':[29],
    'Bad Debt Expense':[31],'Miscellaneous expenses': [33,34,35,36,37],'Marketing Expenses':[40,41,42],
    'Payroll & Related Expenses': [45,46,47,48,49,50,51,52,53,54,55,56], 'Total Utilities':[59,60],
    'Total Equipment Maint, & Rental Expense': [63,64,65,66,67,68],'Total Mill Expense':[70,71,72,73,74,75,76,77],
    'Total Taxes':[80,81],'Total Insurance Expense':[83,84,85],'Incentive Compensation':[88],
    'Strategic Initiative':[89]}

基于主数据帧创建新数据帧

mcon = VA.loc[:,['Expense', 'Mgrl', 'Exp Category', 'Parent Category']]
mcon.loc[:,'Variance Type'] = ['Unfavorable' if x < 0 else 'favorable' for x in mcon['Mgrl']]
mcon.loc[:,'Business Unit'] = 'Managerial Consolidation'
mcon = mcon[['Business Unit', 'Exp Category','Parent Category', 'Expense', 'Mgrl', 'Variance Type']]
mcon.rename(columns={'Mgrl':'Variance'}, inplace=True)

创建最终将写入excel的新数据框

a1 = pd.DataFrame() 
for key, value in d.items():
    umconm = mcon.iloc[value].query('Variance < 0').nsmallest(5, 'Variance')
    fmconm = mcon.iloc[value].query('Variance > 0').nlargest(5, 'Variance')
    if umconm.empty == False or fmconm.empty == False:
        a1 = pd.concat([a1,umconm,fmconm], ignore_index = True)
    else:
        continue
a1.to_csv('example.csv', index = False)

输出如下所示

我试图添加一个新的列，该列显示高于/低于{key}的预算，其中key表示使用以下代码的费用类型

for key, value in d.items():
    umconm = mcon.iloc[value].query('Variance < 0').nsmallest(5, 'Variance')
    umconm.loc[:,'Explanation'] = f'Lower than budgeted {key}'
    fmconm = mcon.iloc[value].query('Variance > 0').nlargest(5, 'Variance')
    fmconm.loc[:,'Explanation'] = f'Higher than budgeted {key}'
    if umconm.empty == False or fmconm.empty == False:
        a1 = pd.concat([a1,umconm,fmconm], ignore_index = True)
    else:
        continue

但是使用上面的字符串文字会给我错误消息“ValueError:无法设置没有定义索引和标量的帧”

如果您能帮我纠正这个问题，或者找到一个不同的解决方案，将这个字段添加到我的数据帧中，我将不胜感激。提前谢谢

Answer 1

发生此错误的原因是该行

umconm = mcon.iloc[value].query('Variance < 0').nsmallest(5, 'Variance')

有时会产生没有索引的空数据帧。当您想要设置列（而不是loc）时，请使用此方法：

a['Explanation'] = f'Lower than budgeted {key}'

Answer 2

我真傻，解决办法如下：

for key, value in d.items():
    umconm = mcon.iloc[value].query('Variance < 0').nsmallest(5, 'Variance')
    umconm['Explanation'] = f'Higher than Budget for {key}'
    fmconm = mcon.iloc[value].query('Variance > 0').nlargest(5, 'Variance')
    fmconm['Explanation'] = f'Lower than Budget for {key}'
    if umconm.empty == False or fmconm.empty == False:
        a1 = pd.concat([a1,umconm,fmconm], ignore_index = True)
    else:
        continue

在这个数据框中创建新列时，我不必使用.loc